The present invention relates generally to vibration control or vehicular suspension systems and, in a preferred embodiment thereof, more particularly provides for a liquid spring vehicular suspension system with an ability to level a vehicle to a desired height, an ability to compensate the level height for the addition or subtraction of load to the vehicle and/or an ability to manage temperature-related changes to fluid volume.
In the past, liquid springs have been used in vibration control or vehicular suspension systems in which the stiffness and damping characteristics of each liquid spring can be adjusted during operation in response to either a sensed variation in the liquid spring or the operating environment. The vibration isolation system could be a vibration control system to protect structures or sensitive machinery from an abusive environment. Alternatively, it could be a vehicular suspension, wherein the characteristics of each liquid spring can be adjusted in response to road conditions or driver inputs. See U.S. Pat. No. 6,305,673, which is incorporated herein by reference. Although the ability to change stiffness and damping is an important property of liquid spring technology, there is a need for additional features to make for a fully functional suspension system.
Among the additional features that can make a suspension system more functional are an ability to level a vehicle or other structure or device to a desired height and to compensate the level height for the addition or subtraction of load as well as other factors. There are liquid spring suspension systems which attempt to provide the desired leveling capabilities, but these systems rely on a central power supply.
The central power supply provides a source and sink of high pressure fluid for use by the system to accommodate the changes in fluid quantity required to accomplish the leveling function. The power supply might include, for example, a hydraulic pump, driven by an electric- or pneumatic-powered motor. The power supply in such a centralized configuration compresses fluid to the appropriate pressure and stores it in an accumulator so that it is readily available to use in any of the multiple struts of the suspension system. The accumulator is required because the actual demand on the power supply is unpredictable. At a given time, any one or more of the struts could require an amount of pressurized fluid. If the hydraulic pump of the power supply were sized to accommodate the requirements of all the struts together, it would be too big for the average demand. The accumulator, therefore, acts in a way to buffer the output of the hydraulic pump and average the peak demand.
The leveling control provides the actuation for leveling and the control of fluid quantity required to set a desired vehicle height at each wheel. This is typically accomplished by having at each wheel a pair of valves, one for leveling up (a fill valve which admits high pressure fluid from the accumulator) and one for leveling down (a dump valve which removes fluid to a low pressure reservoir). These valves act under the command of a signal from some type of controller. The leveling control acts in response to feedback from sensors indicating the current height. By opening a fill valve, the vehicle is raised, while by opening a dump valve, the vehicle is lowered.
A hydraulic harness is a system of tubes which provides a way to transmit the fluid power to and from each wheel. As this harness is required to hold fluid under the pressure of the accumulator charge, its tube components must be able to withstand high pressures. A typical system will have two separate tubes extending to each wheel from the central power supply.
In operation, the fill and dump valves at each wheel are actuated in response to signals from the controller to change the height of the suspension at that wheel. If a fill valve opens, fluid is removed from the accumulator. The motor is switched on by the pressure switch when enough fluid is drawn from the accumulator to reduce the pressure to a certain low pressure. The motor powers the hydraulic pump to charge the accumulator with more fluid, until the pressure switch senses a certain higher pressure, signaling the motor to turn off. This is a traditional architecture for a hydraulically-charged system where the power supply is centralized and runs independently of the load-bearing components, each of which draw power from the central power supply as needed.
There are, however, numerous disadvantages to central power supply systems. With a central power supply, the hydraulic pump must be larger than would be optimal for each individual component of demand, but may not be so large as to handle the rare peak demand. It must also be a high pressure pump, a more expensive form of pump that is more difficult to obtain. Further, a hydraulic harness is necessary. This makes the system difficult to assemble and makes retrofit on an existing vehicle particularly difficult. The extensive hydraulic harness also requires that the suspension system be hydraulically bled after assembly on the vehicle.
It would be desirable to provide a liquid spring vehicular suspension system which has needed leveling ability, but uses a more efficient power supply and/or eliminates the use of an accumulator. One or more embodiments of the present invention provide such a system.